1. Field of the Invention
The present invention relates to a method of manufacturing effectively and economically bulky non-woven fabric having a fluffy structure realized by fiber-raising process carried out during the processing of a non-woven fabric of relatively thin and having a relatively low density. Also, the present invention relates to such bulky non-woven fabric and composite absorbent material to be obtained by said method and absorbent products such as baby and incontinent diapers, feminine hygiene products and medical care products to be made by utilizing such non-woven fabric and composite absorbent material.
2. Related art
Bulky non-woven fabric is used in such uses as filling material, impregnated substrate, foamed substrate and the like as cushioning materials and in addition in many applications such as the top sheet for an absorbent product and a transfer layer and acquisition layer to reinforce an absorbent material.
A variety of methods have been proposed based on various technologies as ways to obtain bulky non-woven fabric of various kind commercially. Such methods are generally classified into six categories as follows:
(1) A method of forming web by means of carded method utilizing so-called bulky fiber such as hollow fiber or hollow bicomponent fiber having coarse denier and high resilience;
(2) A method of imparting a bulky structure by means of forming web consisting potently crimpable and heat shrinkable fibers and heat treating such web so that it becomes crimped and heat shrunk;
(3) A method of imparting a three-dimensional structure by means of continuously folding web oriented in the direction of X-Y like a carded web so that the web is oriented in the direction of Z axis, of then laminating and heat setting the web;
(4) A method of forming a fiber-raised structure by means of physically abrading the surface of non-woven fabric or of transplant;
(5) A method of obtaining bulky tow-like material by means of opening compressed crimped tow in an air stream; and
(6) A method of obtaining a foamed fibrous structure by means of combining a method of manufacturing foamed material such as polyurethane foam, polyethylene foam and cellulose foam with fiber web.
Many of these methods have already been proposed so far. These methods have in common the following two problems in handling such resultant bulky structure:
First, such a structure is bulky for its weight and as such is difficult to be made into a large package so that the cost of handling it in commercial or industrial scenes becomes high. In order to solve such problem, rather complicated operations are needed to wind up it as it is displaced like winding on a bobbin (which is called xe2x80x9cspoolingxe2x80x9d) or heap it as folded (which is called xe2x80x9cfestooningxe2x80x9d).
Second, the characteristic bulkiness of the structure achieved with effort may gradually be reduced as it is handled or further processed.
One of methods thought of in solving these two problems is bulking non-woven fabric in a line of its use when or immediately before it is used so that the resultant bulkiness can be utilized as it is achieved, which is generally called xe2x80x9cin-line bulkingxe2x80x9d.
A typical example of the in-line bulking as reported is that card web pressured and compressed in the shape of mat beforehand is fed continuously into a disposable diaper making machine so that the card web is opened and swollen to make cushion material for baby and incontinent disposable diapers. Alternatively, as reported, shrinkable non-woven fabric is fed as overfed continuously into a heat shrinking machine directly connected to a disposable diaper making machine to cause heat shrinkage corresponding to the amount of the overfeeding in the fabric to make it web material which is, as is made, used as acquisition layer in a baby disposable diaper. An important disadvantage of these solutions is that the equipment of realizing the solutions becomes necessarily complicated and at the same time the difference in speed between the bulking of non-woven fabric and the converting into a disposable diaper can hardly be made up for to synchronize the times.
The present invention has been completed through as the result of intensive research and study intended to overcome the above-mentioned disadvantages of the in-line bulking and to investigate how a compact and efficient process is realized to do so.
The present invention provides a method of bulking a non-woven fabric comprising the steps of:
adhering a non-woven web with its surface layer portion containing an easy-to-heat-melt component showing a property to be adhesive as heated to a smooth surface heated at the temperature for the easy-to-heat-melt component to show a property to be adhesive with said surface layer portion in contact with the smooth surface; and
peeling the non-woven fabric like web off said smooth surface so that a fiber-raised bulky state is generated by fiber-raising the fibers of said non-woven web; whereby a fiber-raised bulky structure is formed on the surface of said non-woven fabric.
In an aspect of the present invention, the adhering step may include a compressively adhering step where the non-woven web is compressively adhered onto the heated smooth surface.
The heated smooth surface may be formed into a cylinder-like shape and in this case, the compressively adhering step is achieved by means of more than one press roll for compressively adhering the non-woven web onto the cylinder-shaped heated smooth surface.
The present invention may include a further step that the non-woven web is preheated by having it pass through a hot air zone before it is introduced into the compressively adhering step.
In addition, the present invention may be provided with an post treatment step where the non-woven web through the fiber-raising step is cooled down so that the already formed fiber-raised structure is fixed.
A further additional step may be a pressing step where the non-woven web is pressed in part to an extent not substantially impairing the fiber-raised structure by pressing a heated roll with projections provided on the fiber-raised surface formed on the non-woven web.
The present invention also provides a method of bulking a non-woven fabric comprising the steps of:
obtaining a non-woven web by providing on the surface of a non-woven fabric a surface layer portion containing an easy-to-heat-melt component exhibiting a property to become adhesive as heated;
obtaining a compressed non-woven fabric by reducing the thickness of the non-woven web by compressing it in the direction of the thickness;
contacting said resultant compressed non-woven fabric with the surface of a roll heated at the temperature for said hot melt adhesive to develop a property to adhere or at higher temperatures and peeling said compressed non-woven fabric off the surface of the roll so as to raise the fiber of said non-woven web; and
stabilizing the fiber-raised bulky structure by subsequently cooling down the fiber-raised portion.
In the present invention, as non-woven web a compressed non-woven fabric can be used as obtained by having non-woven fabric in a dry state with its surface layer portion including an easy-to-heat-melt bicomponent fiber through a heated compression roll so that the thickness is reduced and then cooling it down.
Preferably, the non-woven web is that to be produced by a spun-laced method where a carded web of two layers composed of a surface layer portion mainly consisting of polyethylene terephthalate fiber and a back surface layer mainly consisting of cellulose fiber is formed, entangled integrally in a high pressure water stream and then dried to obtain the non-woven web.
Alternatively, the non-woven web may be such that with a spun bond of polyethylene terephthalate as the basis a mixed carded web of polyethylene/polyethylene terephthalate bicomponent fiber and cellulose fiber is entangled and combined in a high pressure water stream or that with cellulose fiber as the basis, a mixed carded web is entangled and combined in a high pressure water stream consisting of polyethylene/polyethylene terephthalate bicomponent fiber and polyethylene terephthalate fiber.
Another preferable non-woven web used in the present invention is three or four layer composite web consisting of a two-layered spun-bonded web mainly composed of polyethylene terephthalate fiber or polypropylene fiber and a one or two-layered melt-blown web disposed between the two layers of the two-layered spun-bonded web.
In the multi-layered composite web, so-called SMS, SMMS, it is preferable that the two layers of the two-layered spun-bonded web have different deniers, respectively, with the denier of the surface side (d1) being coarser than that of the backside (d2) and with the relation between the denier (d1) and the denier (d2) being
d1/d2xe2x89xa71.5.
More preferably, the two layers of the two-layered spun-bonded web have different apparent specific gravities with the apparent specific gravity of the surface side web (SG1) being higher than that of the backside web (SG2) and with the relation between the bulk specific gravity (SG2) and the bulk specific gravity (SG1) being
SG2/SG1xe2x89xa71.2.
As the fabric-like non-woven web, a spun-bonded or its laminated material whose main component is an easy-to-heat-melt bicomponent fiber can also be used.
In addition, the present invention provides a fiber-raised bulky non-woven fabric characterized in that a non-woven web with a surface layer portion existent on the surface containing an easy-to-heat-melt component having a property to become adhesive as heated is adhered to a smooth surface heated at the temperature at which said easy-to-heat-melt component exhibits a property to become adhesive with said surface layer portion in contact with said smooth surface and then peeled off said smooth surface to generate a fiber-raised bulky state whereby a fiber-raised bulky structure is formed on the surface of said non-woven web.
A preferable easy-to-heat-melt component is, for example, particle, suspension or emulsion of homo-polymer or copolymer of EVA, MA, MMA or PE or natural rubber or synthetic rubber latex.
The easy-to-heat-melt component showing adhesiveness as heated can be a hot melt adhesive.
The easy-to-heat-melt component can be a bicomponent fiber having a property to be easy to heat melt, and in the fiber-raising step a cooling step where the easy-to-heat-melt component is cooled down.
In case the easy-to-heat-melt component is a hot melt adhesive, the amount of added hot melt adhesive is preferably 0.5 to 10% by weight of the total weight of the non-woven web.
The thermal softening point of the hot melt adhesive is preferably at least 20xc2x0 C. lower than the temperature at which the fiber constituting the surface layer of the non-woven fabric starts to melt.
Alternatively, the easy-to-heat-melt component preferably contains a bicomponent fiber consisting of an easy-to-heat-melt high polymer showing a property to be adhesive at the time when it softens and melts and of relatively thermally stable high polymer component.
The content of the bicomponent fiber is preferably 20 to 100% by weight of the total weight of the non-woven web. The bicomponent fiber may be made of a sheath and core structure having a less-easy-to-heat-melt as the sheath and a relatively thermally stable component as the core.
In a further aspect of the present invention, there is provided a method of manufacturing a composite absorbent body comprising the steps of
adhering non-woven web with a surface layer portion existent on the surface containing an easy-to-heat-melt component having a property to become adhesive as heated to a smooth surface heated at the temperature at which said easy-to-heat-melt component exhibits a property to become adhesive with said surface layer portion in contact with said smooth surface;
peeling the non-woven web off said smooth surface to generate a fiber-raised bulky state so as to raise the fibers of said non-woven web; a step of forming non-woven web having a fiber-raised bulky structure on its surface;
applying a highly absorbent polymer in slurry to the fiber-raised bulky surface of the non-woven web obtained in the previous step used as a substrate to make a composite; and
removing dispersion medium out of said slurry so that the highly absorbent polymer is fixed in the non-woven web.
According to another aspect of the present invention is provided an absorbent product wherein on the surface of non-woven web are provided a non-woven web having a fiber-raised bulky structure on its surface and an absorbent body, said non-woven web being obtained through a adhering step of adhering non-woven web with a surface layer portion existent on the surface containing an easy-to-heat-melt component having a property to become adhesive as heated to a smooth surface heated at the temperature at which said easy-to-heat-melt component exhibits a property to become adhesive with said surface layer portion in contact with said smooth surface and a fiber-raising step of then peeling the non-woven web off said smooth surface to generate a fiber-raised bulky state, and said fiber-raised bulky non-woven fabric being disposed with fiber-raised surface having a cushion property facing said absorbent body and its smooth backside functioning as a topsheet in contact with the body of a wearer.
In such absorbent product the fiber-raised bulky non-woven fabric has preferably such a porous structure on the smooth backside as permit liquid to physically permeate.
According to still another aspect of the present invention is provided an absorbent product wherein a substrate consisting of non-woven web having a fiber-raised bulky structure on its surface and an absorbent body consisting of a highly absorbent composite where the substrate and a particulate highly absorbent polymer are integrated, said non-woven web being obtained through a adhering step of adhering non-woven web with a surface layer portion existent on the surface containing an easy-to-heat-melt component having a property to become adhesive as heated to a smooth surface heated at the temperature at which said easy-to-heat-melt component exhibits a property to become adhesive with said surface layer portion in contact with said smooth surface and a fiber-raising step of then peeling the non-woven web off said smooth surface to generate a fiber-raised bulky state.
In this absorbent product, the highly absorbent composite body can be used as the backsheet as provided with water impermeability with the non-woven web containing the easy-to-heat-melt component being liquid impervious and water resistance and with the highly absorbent resin made in an integral composite with the fiber-raised surface of the non-woven web.
The present invention provides a method of manufacturing an absorbent product comprising the steps of:
adhering non-woven web with a surface layer portion existent on the surface containing an easy-to-heat-melt component having a property to become adhesive as heated to a smooth surface heated at the temperature at which said easy-to-heat-melt component exhibits a property to become adhesive with said surface layer portion in contact with said smooth surface, a fiber-raising step of then peeling the non-woven web off said smooth surface to generate a fiber-raised bulky state, and
forming non-woven web having a fiber-raised bulky structure on its surface, and a step of incorporating the non-woven web obtained in the previous step into an absorbent product.
According to the present invention, since a non-woven web with a surface layer portion disposed on its surface containing an easy-to-heat-melt component having a property to be adhesive as heated is adhered to a smooth surface heated to a temperature at which the easy-to-heat-melt component becomes adhesive in contact with the surface layer portion, and peeled off the smooth surface so that a fiber-raised bulky state is generated, the non-woven web can be fed as being made bulky directly connected to a disposable diaper making machine so that the non-woven web as it is can be used as a component material of a diaper whereby the method of making a diaper can be simplified equipment-wise and process-wise and the speed of the diaper making line can be made higher.
In addition, bulky non-woven fabric to be obtained by the methods of the present invention can be advantageously used as topsheet for an absorbent article and as transfer and acquisition layers to reinforce an absorbent body in such a variety of uses as contain absorbent products like disposable baby and incontinent diapers, feminine hygiene articles and medical care products.